The RFID (radio frequency identification) technique that has recently been developed rapidly is a system wherein a radio transmitter/receiver called a reader/writer reads or writes information into or from, tags incorporating therein information memory devices without physical contact. This system, different from the bar-code reader or the magnetic card reader which needs physical contact, will be seldom affected by adverse surface conditions such as smears or blots. Also, with this system, reading/writing operation will be much simplified since for desired operations such tags have only to be placed or passed within a space which the reader/writer can cover in radio communication. Moreover, this system is advantageous over the bar-code technique in that since each tag may be provided with its individual ID, the system may hold much more storable information than the bar-code scheme. Accordingly, the RFID system has been regarded as a long-desired memory device and its application is becoming yet wider in various fields.
Cables laid in a plant or a railroad system have generally had their structure, material, and specification determined depending on their applications to power supply, signal detection or equipment control; the relationship between their service environments and useful life; and their costs. Most often used cables, however, are limited in their type, that is, only several types of cables are preferably used in most applications. They look all alike and therefore it is difficult to distinguish one from another by visual inspection alone.
In order to facilitate differentiation, various ideas have been reduced to practice: codes have been printed or labels have been stuck, onto cable surface or tags have been stringed to cable body. Such ideas include the printing of codes on the surface of cable at regular intervals in the manufacturing process for cable type identification and the tagging of cable with such information as cable number, start point of cable, end point of cable, etc. for individual differentiation.
Surface printing has a problem that the printed codes are subjected to abrasion or smearing during handling of cable in its layout operations. Tagging is risky in that tags may be torn off the cable during laying work, and also has a problem that since tagging is more laborious than printing, the provision of cable with tags at regular intervals for facility of identification will cause an increase in cost as the length of cable increases.
To solve a problem of how inexpensively and accurately one cable should be differentiated from another, JP-A-H07-211158 document discloses a cable structure wherein both resonant elements resonating with a radio signal having a predetermined frequency and information storage elements storing name data therein are introduced in the cable accommodating space.
In addition, JP-A-2004-139535 document discloses a cable structure wherein more than two information storage elements are arranged at intervals along the cable in its lengthwise direction and the elements are connected in series with one another with communication lines.
These cable structures still have room for improvement in that somewhat laborious work is necessary to record such information as names in the information storage elements whose number increases in proportion as the length of cable increases.